Scientists find that the nose knows a lot

March 19, 2008

Dogs sniff out their path. Ants follow scent trails. Chemical navigation is a familiar animal skill. Yet its subtleties continue to amaze biologists. New research shows, for the first time, how the albatross smells out food as it glides above the sea. Another study reveals that marine sulfur compounds, whose effect on climate influences global warming, also give off odors that play an unexpected role in the ecology of healthy coral reefs.

As detailed in the team's paper published earlier this month in the Proceedings of the National Academy of Sciences online, individual birds were fitted with instruments while they nested on Possession Island in the Indian Ocean. GPS receivers recorded their location every 10 seconds while stomach temperature gauges marked every meal. The data were recovered when the birds returned to their nesting sites.

Albatrosses feed on dead squid and other floating carrion as they fly low over the sea. Looking at the recovered data, the members of this international research team found strong evidence that the birds use their sense of smell to guide them to carrion that may be several miles away. That's beyond the birds' visual horizon. The birds tended to fly across the wind, a good way to pick up an odor trail while conserving flight energy. Other flight patterns also indicate that they were following scent plumes. Professor Nevitt says that the albatross's flight strategy lets it cover a swath several miles wide.

Meanwhile, Nevitt joined colleagues at UC Davis in researching an unsuspected aspect of a much-studied marine chemical. Its chemical name is so complex that everyone just calls it DMSP. Algae and other microscopic marine plants release it. In the atmosphere, DMSP breaks down into sulfur compounds that form cloud particles that, in turn, reflect sunshine back into space. This is a cooling effect that can moderate global warming.

As they explained in their report in Science magazine on March 7, however, those sulfur compounds also act as odor signals in the sea. They indicate that tiny animals are eating the algae or that the algae themselves have formed a large bloom. Either way, the odors could indicate to sea life that something of interest is going on. They are not smelling food directly. They are picking up clues that indicate they should check out the odor's source.

The research team tested this by releasing DMSP at a coral reef. Team member Jennifer DeBose says the result "was pretty impressive." They would be "surrounded by hundreds of fish for up to 60 minutes." One-celled organisms that live within the reefs give off DMSP. When corals are ill, they lose these organisms, become bleached, and die. Thus, Nevitt explains, "DMSP is the smell of a productive, healthy reef."

We take the sense of smell for granted. Yet we have scarcely begun to understand the roles it plays at many levels in the biology of planet Earth.